The present invention relates to a vinylpyrrolidone-based polymer composition, more precisely to a vinylpyrrolidone-based polymer composition which has improved storage stability and of which the reduction in the molecular weight (K value) under shear stress is small.
A vinylpyrrolidone-based polymer (PVP) such as polyvinylpyrrolidone and vinylpyrrolidone copolymer has characteristics of biocompatibility, safety and hydrophilicity, and is therefore widely used for substrates for cosmetics and for binders for medicines.
In general, PVP is obtained through solution polymerization, and it may be stored directly as its solution or, after dried and ground, it may be stored as a solid. However, irrespective of its morphology, it is known that the storage stability of PVP is generally poor; and for example, when it is stored for a long period of time or at a high temperature, it has a problem in that its physical properties such as molecular weight may change with time.
In case where solid PVP is ground and used as its powder, its molecular weight may lower when large shear stress is applied to PVP in its grinding step, and therefore the grinding condition is limited and the powdering capability and the grinding efficiency may be thereby worsened. Regarding solution PVP, for example, when an emulsion of an aqueous PVP solution is prepared, it requires high-speed stirring; however, it is problematic in that the molecular weight of PVP shall lower under shear stress during high-speed stirring, and the emulsion therefore could not have the necessary viscosity.
For improving the storage stability of the above PVP, JP-A 2003-138087 discloses a technique of adding any of guanidines or biguanides to PVP.
According to the technique described in JP-A 2003-138087, they say that adding any of guanidines and/or biguanides to PVP improves the stability of PVP, therefore improving the storage stability thereof; however, the technique is still ineffective for preventing the reduction in the molecular weight of PVP under stress given thereto during grinding and stirring it.